The US electoral college has certified Donald Trump as the 45th president, despite a last-ditch effort to deny him the White House.

Six weeks after winning the polls, the Republican cruised past the 270 votes needed to formalise his victory.

After the result, Mr Trump promised to "work hard to unite our country and be the president of all Americans".

Electors had been flooded with emails and phone calls urging them not to support the billionaire.

But despite longshot liberal hopes of a revolt by Republican electors, only two - from Texas - ended up voting against him.